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Appendix VL                            1121

Dohmen-Leblanc coupling, Fig. 989, is also for gripping only.
The drum B is carried on the shaft A, and the disc c on the shaft K,
while gripping jaws D D with corrugated surfaces slide in guides
formed on the disc. These grips are connected to the lever boss
E by stout flat springs F F, that force the parts D and B into
contact when E is moved leftward. The interesting point in this,
clutch is that when the boss E is moved hard over, the pin G gets
past the vertical through H, and so locks the clutch parts as to
prevent any tendency to release when driving,

The remaining diagrams illustrate the newest forms of clutch,
suitable both for hard grip and for the most sensitive slipping,
The Hele-Shaw clutch, Fig, 990, consists of a solid drum E keyed
to the,shaft A, and a hollow drum c with sides B and D, the part
D being keyed to the other shaft F. The drum E is supplied with
teeth a, and the drum c with teeth b ; and of the discs G, half are
fixed to one drum, while the alternate half are keyed to the other
drum. /The discs are provided with circular wedge-form corru-
gations, each containing an angle of about 35, and the gripping
is obtained as in the Weston clutch by pressing the discs together
by means of the plate H. The boss K causes the pressing action
through the pins P, but the lever ring M only does this indirectly
at first. Moving M leftward it first tilts the small levers L till it
falls into the hole D, thus permitting the compressed spring j to
expand and press K and P upon plate H. Further pressure can
now be obtained by ring M on the boss K. To disengage, the
lever moves M rightward, and the levers L fall out of gear by the
action of spring N, thus keeping the clutch out of gear. The Coil
Clutch, Fig. 991, is both simple and effective. The drum B is
fixed to shaft A, and carries a disc c, through which passes the
lever boss D. A drum F is keyed to the other shaft E, and a
coiled spring G lies loosely upon it, being anchored by the eye H
to pin L in the drum. A lever M, centred on the pin N in the
disc c, is moved radially when acted on by the boss p, and then
engages the lug j on the other end of the coil, causing it to grip
upon the drum F. The grip of such a coil, as is well-known, is
considerable, even though the tension may be slight, and there is
no tendency to release in the design shewn because the lever lies
in the parallel portion of D when in full action. TMs clutch will